The present invention relates to precast building construction and, more particularly, to a relatively simple and inexpensive method of forming a concrete building with precast wall and floor panels which results in a unitized building capable of effectively resisting vertical and horizontal loads.
Multi-story concrete buildings are generally formed by casting in place both the floors and the supporting walls. That is, a floor slab providing the floor for each story is formed or raised into place, and then the concrete walls for such story are poured directly at the location at which they will appear in the building. This method of construction has been followed to assure that the physical connection between the walls and floors will be of sufficient structural strength to resist the vertical and horizontal forces to which it may be subjected, such as by an earthquake. However, such a method of construction requires a significant labor force and a time-consuming procedure. The result is that this type of concrete building construction is relatively expensive.
In order to circumvent the expense involved in such a construction, those in the art have turned in many instances to other types of construction. One type is the so-called "tilt-up" method of construction. In such a method, the walls are formed in sections prior to the time the building is to be erected, and then are tilted vertically into the location desired for them. Generally, such an erected wall is tied to the building floor slab by either forming a concrete beam encompassing its lower edge or by having the floor slab poured around the bottom of the wall after it is erected. The difficulty with tilt-up construction, though, is that its use is generally limited to one-story buildings since the tilt-up walls typically are perimeter walls. Moreover, mechanical connectors of one sort or another are generally required to connect adjacent wall sections together and to structurally connect such walls to a later applied roof. Such connectors are often complicated and require an inordinate amount of installation time.
Another type of construction relies on factory built panels to construct the walls and/or floors of a concrete building. Factory built concrete components are becoming increasingly expensive, however, primarily due to fuel and transportation costs. Moreover, with most of such systems an additional concrete slab must be poured on top of the precast slabs at the site for each of the floors to tie the precast components together. Thus, this method does not significantly circumvent the labor force and long procedure required in poured-in-place construction. Intensive mechanical connections or welding are also often required in such methods to tie the concrete components together.
One other approach which has been proposed and used in the past to construct multi-story buildings is one in which precast wall panels are provided with voids and then interlocked to a floor slab by having reinforcing dowels or rods or the like extending upward from the floor slab project into such voids. Additional reinforcing rods are then introduced into the voids to overlap the ones projecting upward from the floor, and the voids are filled with grout. While this approach to multi-story construction provides sufficient structural integrity to resist any vertical loads to which the connection between the wall panels and floor slabs are subjected, it does not provide the resistance against horizontal shear which is necessary in active seismic areas. And again, the floor slabs are poured in place with the resulting expense and time consuming procedure associated therewith.